A separation principle associated with sensor time delay compensation in feedback control

Motivated by recent research into the automation of radiotherapy for the treatment of cancer, this paper looks at feedback control problems where the feedback sensor introduces a time delay. As in previous work, the use of an asymptotic estimator (for example, an observer-based estimator) is considered as a method of compensating for the sensor time delay. The main result in this paper is that, if such a delay compensation strategy is used, a separation principle holds which allows the designer to independently design the feedback controller and the time-delay compensator. The radiotherapy problem is used as a case study to show how the separation principle can be exploited in design.